crjdriver is one of the respected hardware/gaming experts here, so I'll leave you with him about the graphic card and power supply.
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I want to mention something though that probably will contribute to slowness and shutdown issues with that computer if it isn't dealt with.
The heat sink/cooling fan unit over the processor is very clogged with dust and needs to be cleaned out.
View attachment 255553
This is going to prevent the processor from staying cool enough.
When the processor overheats, it slows down to prevent getting damaged, which in turn makes the computer run slower.
If the processor gets too hot, the computer will freeze up or shut down.
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